TW201924127A - Lithium secondary battery and device for manufacturing built-in battery - Google Patents

Abstract

The present invention provides a lithium secondary battery excellent in heat resistance. The lithium secondary battery includes a lithium composite oxide sintered plate, that is, a positive plate, a negative electrode containing carbon and styrene butadiene rubber (SBR), and is composed of γ-butyrolactone (GBL) or is composed of γ-butyl An electrolyte containing lithium tetrafluoroborate (LiBF ₄ ) in a non-aqueous solvent composed of lactone (GBL) and ethyl carbonate (EC).

Description

Manufacturing method of lithium secondary battery and device with built-in battery

The invention relates to a method for manufacturing a lithium secondary battery and a device with a built-in battery.

In recent years, smart cards with built-in batteries are becoming more practical. An example of a smart card with a built-in battery is a credit card with a one-time password display function. Examples of smart cards with built-in secondary batteries include wireless communication ICs, fingerprint analysis ASICs, and fingerprint sensors with fingerprint verification and wireless communication functions as examples. Generally, the smart card battery requires characteristics such as a thickness of less than 0.45 mm, high capacity, low resistance, resistance to bending, and resistance to program temperature.

Liquid thin-film lithium batteries suitable for this purpose have been proposed. For example, in Patent Document 1 (Japanese Patent Laid-Open Publication No. 2013-97931) and Patent Document 2 (Japanese Patent Laid-Open Publication No. 2012-209124), a battery having an outer-layer coating film is disclosed. The battery has a positive electrode current collector. The electrode laminate of the positive electrode, the separator, the negative electrode, and the negative electrode current collector is housed in a laminated film container and sealed. The batteries disclosed in Patent Documents 1 and 2 are all lithium primary batteries.

The positive electrode active material layer for lithium secondary batteries (also known as lithium ion secondary batteries) is widely known as adding powders of lithium composite oxides (typically lithium transition metal oxides), binders, and conductive agents. A powder-dispersed positive electrode obtained by kneading and shaping materials. Since this powder-dispersed positive electrode contains a large amount (for example, about 10% by weight) of a binder which is not beneficial to the capacity, the lithium composite oxide as a positive electrode active material has a low packing density. Therefore, there is much room for improvement in the capacity and charge / discharge efficiency of the powder-dispersed positive electrode. Therefore, attempts have been made to improve the capacity and charge / discharge efficiency by using a lithium composite oxide sintered plate to form a positive electrode or even a positive electrode active material layer. At this time, since the positive electrode or the positive electrode active material layer does not contain a binder, it is expected to obtain a high capacity and good charge-discharge efficiency by increasing the filling density of the lithium composite oxide. For example, Patent Document 3 (Japanese Patent Publication No. 5587052) discloses a positive electrode of a lithium secondary battery having a positive electrode current collector and a positive electrode active material layer bonded to the positive electrode current collector via a conductive bonding layer. The positive electrode active material layer is composed of a lithium composite oxide sintered plate having a thickness of 30 μm or more, a porosity of 3 to 30%, and an open porosity of 70% or more.

In addition, Patent Document 4 (Japanese Patent Laid-Open Publication No. Hei 10-312825) discloses a lithium secondary battery. In order to improve low-temperature discharge characteristics, a lithium secondary battery using 10 to 40% by volume of ethyl carbonate and A mixed solvent composed of 60-90% by volume of γ-butyrolactone is used as a non-aqueous solvent for the electrolytic solution.
[Prior technical literature]
[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2013-97931
[Patent Document 2] Japanese Patent Laid-Open Publication No. 2012-209124
[Patent Document 3] Japanese Patent Gazette No. 5587052
[Patent Document 4] Japanese Patent Laid-Open Publication No. 10-312825

In the manufacture of cards, thermal lamination may be performed. For example, a card for thermal lamination is manufactured by pressing and bonding a card substrate and a resin film at a temperature of 110 ° C or higher (for example, 120 to 150 ° C). get on. For this reason, the method of making a thin lithium battery built into a thin device such as a smart card is suitable as long as it can be processed by thermal lamination. At this time, it is considered that a thin lithium battery and a protective film are sequentially laminated on the card substrate and pressurized at a high temperature of 110 ° C or higher. However, the conventional liquid thin lithium battery has insufficient heat resistance, and when heated above 110 ° C, it will cause the battery to swell and break, and increase the battery resistance. On the other hand, the method of installing a thin lithium battery on a printed wiring board is considered a procedure with reflow soldering. However, this method may also be heated to a high temperature, so the same problem may occur as described above.

The inventors of the present case have obtained the following insights. The foregoing insights are obtained by selectively combining a lithium composite oxide sintered plate, that is, a positive electrode plate, a negative electrode containing carbon and styrene butadiene rubber (SBR), An electrolytic solution containing lithium tetrafluoroborate (LiBF ₄ ) in a non-aqueous solvent composed of an ester (GBL) and optionally ethyl carbonate (EC) can provide a lithium secondary battery having excellent heat resistance.

Therefore, an object of the present invention is to provide a lithium secondary battery having excellent heat resistance.

According to an aspect of the present invention, there is provided a lithium secondary battery including a lithium composite oxide sintered plate, that is, a positive electrode plate, a negative electrode containing carbon and styrene butadiene rubber (SBR), and a γ-butyrolactone Electrolyte containing lithium tetrafluoroborate (LiBF ₄₎ in a non-aqueous solvent consisting of (GBL) or γ-butyrolactone (GBL) and ethyl carbonate (EC).

According to another aspect of the present invention, a method for manufacturing a built-in battery device is provided, including the following processes: (1) preparing the lithium secondary battery; (2) passing the lithium secondary battery through The heating process at 260 ° C was mounted on the substrate.

[Forms for Implementing Invention]

An example of the lithium secondary battery of the present invention is schematically shown in FIG. 1. The lithium secondary battery 10 shown in FIG. 1 includes a positive electrode plate 16, a negative electrode 20, and an electrolytic solution 24. The positive electrode plate 16 is a lithium composite oxide sintered plate. The negative electrode 20 includes carbon and styrene butadiene rubber (SBR). The electrolyte 24 contains lithium tetrafluoroborate (LiBF ₄ ) in a non-aqueous solvent composed of γ-butyrolactone (GBL), and optionally, ethyl carbonate (EC). In this way, by selectively combining a lithium composite oxide sintered plate, that is, a positive electrode plate 16, a negative electrode 20 containing carbon and styrene butadiene rubber (SBR), and optionally a γ-butyrolactone (GBL), An electrolyte 24 containing lithium tetrafluoroborate (LiBF ₄ ) in a non-aqueous solvent composed of ethylene carbonate (EC) can provide a lithium secondary electrode having excellent heat resistance. In addition, in FIG. 1, a plurality of small plate-shaped positive electrode plates 16 are shown. The present invention is not limited to this, and one positive plate 16 that is not divided into small pieces may be used.

As mentioned above, the method of making thin lithium batteries built into thin devices such as smart cards considers thermal lamination. In addition, a method for mounting a thin lithium battery on a printed wiring board is considered a procedure with reflow soldering. These methods will all heat to a high temperature above 110 ° C, but the conventional liquid thin lithium battery has insufficient heat resistance. When heated above 110 ° C, it will cause the battery to expand and break, and increase the battery resistance. On the other hand, the lithium secondary battery 10 of the present invention has excellent heat resistance such that the battery does not swell and break even when heated to 110 ° C or higher, and does not show an increase in battery resistance. This excellent heat resistance is brought about by selectively employing the above-mentioned members as constituent elements of the positive electrode plate 16, the negative electrode 20, and the electrolytic solution 24.

Therefore, the lithium secondary battery 10 is preferably scheduled to be mounted on the substrate by a procedure having a heating of 110 ° C. or higher, and the above-mentioned procedure with heating is preferably a process of thermal lamination or a procedure with reflow. In other words, according to another preferred aspect of the present invention, a method for manufacturing a built-in battery device is provided, which includes a process of preparing a lithium secondary battery, and mounting the lithium secondary battery on a substrate through a process having a heating of 110 ° C or higher. The manufacturing process is preferably a heat lamination process or a process with reflow. At this time, it is particularly preferable to use a smart card with a built-in battery that is a thermal lamination process with a heating program. In any aspect, the preferred heating temperature is above 110 ° C and below 260 ° C, more preferably above 110 ° C and below 240 ° C, even more preferably above 110 ° C and below 220 ° C, and particularly preferably 110 ° C. Above, it is less than 200 ° C, more preferably 110 ° C or more and less than 150 ° C.

The positive electrode plate 16 is a lithium composite oxide sintered plate. The fact that the positive plate 16 is a sintered plate means that the positive plate 16 does not contain a binder. This is because even if the raw embryo contains a binder, the binder will disappear or burn out during firing. Furthermore, since the positive electrode plate 16 does not contain a binder, there is an advantage that deterioration of the positive electrode caused by the electrode liquid can be avoided. For example, as disclosed in Patent Documents 1, 2, and 4, the conventional lithium battery positive electrode has widely used a binder such as polydifluoroethylene (PVDF), and this PVDF is easily dissolved in the electrolyte used in the present invention. Γ-butyrolactone (GBL), which deteriorates the function as a binder. In this regard, since the positive electrode plate 16 used in the present invention is a sintered body that does not contain such a binder, the above problems are not caused. In addition, the lithium composite oxide constituting the sintered plate is particularly preferably lithium cobaltate (typically, LiCoO ₂ (hereinafter referred to as LCO)). Various lithium composite oxide sintered plates and even LCO sintered plates are known, and those disclosed in, for example, Patent Document 3 (Japanese Patent Publication No. 5587052) can be used.

According to a preferred aspect of the present invention, the positive electrode plate 16, that is, the lithium composite oxide sintered plate is a directional positive electrode plate, which contains a plurality of primary particles composed of a lithium composite oxide, and the plurality of primary particles are on the plate surface of the positive electrode plate. More than 0303 shows an example of a cross-sectional SEM image perpendicular to the plane of the directional positive electrode plate 16. On the other hand, FIG. 4 shows electron backscatter diffraction (EBSD: Electron Backscatter) Diffraction) like. FIG. 5 shows a histogram showing the distribution of the orientation angle of the primary particles 11 of the EBSD image of FIG. 4 on an area basis. In the EBSD image shown in Fig. 4, the discontinuity of crystal orientation can be observed. In FIG. 4, the orientation angle of each primary particle 11 is displayed by the color depth. The darker the color, the smaller the display orientation angle. The orientation angle refers to an inclination angle formed by (003) of each of the primary particles 11 facing the plate surface direction. In addition, in FIG. 3 and FIG. 4, the place shown in black inside the directional positive electrode plate 16 is an air hole.

The oriented positive electrode plate 16 is an oriented sintered body composed of a plurality of primary particles 11 bonded to each other. Each primary particle 11 is mainly plate-shaped, and may include primary particles formed into a rectangular parallelepiped shape, a cubic shape, a spherical shape, or the like. The cross-sectional shape of each primary particle 11 is not particularly limited, and may be a rectangle, a polygon other than a rectangle, a circle, an ellipse, or a complex shape other than these.

Each primary particle 11 is composed of a lithium composite oxide. The lithium composite oxide refers to an oxide represented by Li _x MO ₂ (0.05 <x <1.10, M is at least one transition metal, and M typically includes one or more of Co, Ni, and Mn). The lithium composite oxide has a layered rock salt structure. Layered rock salt structure refers to the crystalline structure in which the lithium layer and the transition metal layer other than lithium are alternately laminated through the oxygen layer, that is, the crystalline structure in which the transition metal ion layer and the lithium alone layer are alternately laminated through the oxide ion (typically α-NaFeO ₂ structure, that is, the structure where the transition metal and lithium are regularly arranged in the [111] axis direction of the cubic salt structure. Examples of the lithium composite oxide include Li _x CoO ₂ (lithium cobaltate), Li _x NiO ₂ (lithium nickelate), Li _x MnO ₂ (lithium manganate), Li _x NiMnO ₂ (lithium nickel manganate), Li _x NiCoO ₂ (lithium nickel cobaltate), Li _x CoNiMnO ₂ (lithium nickel cobalt manganate), Li _x CoMnO ₂ (lithium cobalt manganate), etc., for example, Li _x CoO ₂ (lithium cobaltate, representative The property is LiCoO ₂ ). The lithium composite oxide may also contain Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Ag, Sn, Sb, Te, Ba, Bi, and W are selected from one or more elements.

As shown in FIGS. 4 and 5, the average value of the orientation angles of the primary particles 11, that is, the average orientation angle is more than 0301. Since each primary particle 11 is in a state of tilting in a direction inclined to the thickness direction, it is possible to make each The adhesion between the primary particles is improved. As a result, the lithium ion conductivity between one primary particle 11 and other primary particles 11 adjacent to both sides of the length of the primary particle 11 can be improved, so that the rate characteristics can be improved. Second, the rate characteristics can be further improved. This is because, as described above, when the lithium ions are in and out, the positive electrode plate 16 has an advantage of expansion and contraction in the thickness direction compared to the plate surface direction. Therefore, the expansion and contraction of the positive electrode plate 16 is smooth. As a result, the lithium ion Followed by smooth.

The average orientation angle of the primary particles 11 is obtained by the following method. First, in an EBSD image observed at a magnification of 1000 times in a rectangular region of 95 μm × 125 μm as shown in FIG. 4, three horizontal lines that align the positive electrode plate 16 in the thickness direction are drawn, and the positive electrode plate is oriented 16 three quarter lines in the direction of the board surface. Next, by averaging the orientation angles of all the primary particles 11 that intersect with at least one of the three horizontal and three vertical lines, the average orientation angle of the primary particles 11 is obtained. The average orientation angle of the primary particles 11 is preferably 302511 from the viewpoint of more improved rate characteristics, and the average orientation angle of the primary particles 11 is preferably 25 from the viewpoint of more improved rate characteristics.

As shown in FIG. 5, the orientation angle of each primary particle 11 can also be analyzed from the oriented sintered body of 09003016 by EBSD. The orientation angle of the primary particles 11 included in the analyzed section to the plane of the oriented positive electrode plate 16 The total area of more than 03011 (hereinafter referred to as low-angle primary particles) is preferably 70% or more, and 80% of the total area of the primary particles 11 (specifically 30 primary particles used to calculate the average orientation angle) included in the cross section. The above is better. Thereby, since the ratio of the primary particles 11 having high mutual adhesion can be increased, the rate characteristics can be further improved. The orientation angle of the low-angle primary particles is 2030, and the total area of the primary particles 11 is preferably 50% or more. Furthermore, it is preferable that the total area of the primary particles 11 with the orientation angle of 1030 primary particles 11 in the low-angle primary particles is 15% or more.

Since each primary particle 11 is mainly plate-shaped, as shown in FIG. 3 and FIG. 4, the cross-section of each primary particle 11 extends in a predetermined direction, and is typically formed into a substantially rectangular shape. That is, when the sintered body is analyzed for its cross section by EBSD, the total area of the primary particles 11 having an aspect ratio of 4 or more among the primary particles 11 included in the analyzed cross section is compared with the primary particles 11 included in the cross section (specifically used for average The total area of the 30 primary particles 11) calculated from the orientation angle is preferably 70% or more, and more preferably 80% or more. Specifically, in the EBSD image shown in FIG. 4, the adhesion between the primary particles 11 can be further improved. As a result, the rate characteristics can be further improved. The aspect ratio of the primary particle 11 is a value obtained by dividing the maximum phenanthrene diameter of the primary particle 11 by the minimum phenanthrene diameter. The maximum Philippine diameter is the maximum distance between the straight lines when the primary particle 11 is sandwiched by two parallel straight lines on the EBSD image when the cross section is observed. The minimum Philae diameter is the minimum distance between the straight lines when the primary particle 11 is sandwiched by two parallel straight lines on the EBSD image.

The average particle diameter of the plurality of primary particles constituting the sintered body is preferably 5 μm or more. Specifically, the average particle diameter of the 30 primary particles 11 used for calculating the average orientation angle is preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 12 μm or more. Thereby, since the number of grain boundaries of the primary particles 11 in the direction of lithium ion transmission is reduced, and the overall lithium ion conductivity is improved, the rate characteristics can be further improved. The average particle diameter of the primary particles 11 is a value obtained by arithmetically averaging the projected area diameter of each primary particle 11. The projected area diameter refers to the diameter of a circle having the same area as each primary particle 11 on the EBSD image.

The density of the oriented sintered body constituting the oriented positive electrode plate 16 is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. Accordingly, since the adhesion between the primary particles 11 can be further improved, the rate characteristics can be further improved. The denseness of the sintered compact was calculated by grinding the cross section of the positive electrode plate by CP grinding (ion beam cross-section grinding), observing the SEM at 1000 times, and binarizing the obtained SEM image. The average projected area diameter of the pores formed inside the sintered compact is not particularly limited, but is preferably 8 μm or less. The smaller the average projected area diameter of each pore, the more the primary particles 11 can adhere to each other. As a result, the rate characteristics can be further improved. The average projected area diameter of the pores is an arithmetic average of the projected area diameters of the ten pores on the EBSD image. The projected area diameter refers to the diameter of a circle having the same area as each air hole on the EBSD image. Each of the pores formed inside the directional sintered body may also be an open pore connected to the outside of the directional positive electrode plate 16, and preferably does not penetrate the directional positive electrode plate 16. In addition, each air hole may be a closed air hole.

From the viewpoint of increasing the active material capacity per unit area and increasing the energy density of the lithium secondary battery 10, the thickness of the oriented positive electrode plate 16 is preferably 30 μm or more, more preferably 40 μm or more, and particularly preferably 50 μm or more. 55 μm or more is the best. The upper limit of the thickness is not particularly limited. From the viewpoint of suppressing deterioration of battery characteristics (especially an increase in resistance value) caused by repeated charge and discharge, the thickness of the oriented positive electrode plate 16 should be less than 200 μm, and 150 μm or less as Preferably, it is more preferably 120 μm or less, particularly preferably 100 μm or less, and most preferably 90 μm or less, 80 μm or less, or 70 μm or less. In addition, the size of the directional positive electrode plate is preferably 5mm × 5mm square or more, more preferably 10mm × 10mm ~ 200mm × 200mm square, more preferably 10mm × 10mm ~ 100mm × 100mm square, and another presentation method is 25mm more preferably ² to 100 ~ 40000mm ² is preferred, in order to more preferably 100 ~ 10000mm ^2.

The negative electrode 20 contains carbon and a styrene butadiene rubber (SBR). That is, carbon is a negative electrode active material, and SBR is a binder. Examples of carbon include black lead (graphite), pyrolytic carbon, coke, resin fired body, mesophase carbon microspheres, and mesophase pitch. Black lead is preferred. Black lead may be either natural black lead or artificial black lead. The negative electrode 20 has the advantage that the deterioration of the negative electrode caused by the electrolytic solution can be avoided by containing a styrene butadiene rubber (SBR) as a binder. For example, as disclosed in Patent Document 4, in the negative electrode of conventional lithium batteries, a binder such as polydifluoroethylene (PVDF) is widely used, and this PVDF is easily dissolved in γ- used in the electrolytic solution of the present invention. Butyrolactone (GBL) deteriorates its function as a binder. In this regard, since the negative electrode 20 used in the present invention selectively uses a styrene butadiene rubber (SBR) that is not easily soluble in GBL, the above-mentioned problems are not caused. Therefore, the negative electrode 20 is preferably free of a binder other than SBR (for example, PVDF).

The electrolytic solution 24 contains lithium tetrafluoroborate (LiBF ₄ ) in a non-aqueous solvent. The non-aqueous solvent may be a separate solvent composed of γ-butyrolactone (GBL), or a mixed solvent composed of γ-butyrolactone (GBL) and ethyl carbonate (EC). By containing γ-butyrolactone (GBL), the non-aqueous solvent raises the boiling point and brings about a significant improvement in heat resistance. From this point of view, the EC: GBL volume ratio of the non-aqueous solvent should be 0: 1 ~ 1: 1 (GBL ratio 50 ~ 100% by volume), and 0: 1 ~ 1: 1.5 (GBL ratio 60 ~ 100% by volume). ) Is more preferable, and 0: 1 to 1: 2 (GBL ratio of 66.6 to 100% by volume) is more preferable, and 0: 1 to 1: 3 (GBL ratio of 75 to 100% by volume) is particularly preferable. Lithium tetrafluoroborate (LiBF ₄ ), which is dissolved in a non-aqueous solvent, is an electrolyte with a high decomposition temperature, which also brings a significant improvement in heat resistance. The concentration of LiBF ₄ in the electrolytic solution 24 is preferably 0.5 to 2 mol / L, more preferably 0.6 to 1.9 mol / L, more preferably 0.7 to 1.7 mol / L, and particularly preferably 0.8 to 1.5 mol / L.

The electrolytic solution 24 preferably further contains vinylene carbonate ((VC) and / or fluoroethylene carbonate (FEC) and / or ethylene ethylene carbonate (VEC) as additives. Both VC and FEC are excellent in heat resistance. Therefore, borrowing The electrolytic solution 24 contains such an additive, and can form an SEI film having excellent heat resistance on the surface of the negative electrode 20, thereby further improving the heat resistance of the lithium secondary battery 10.

The lithium secondary battery 10 preferably further includes a separator 18. The separator 18 is preferably a separator made of polyimide, polyester (such as polyethylene terephthalate (PET)), or cellulose, and a separator made of polyimide is more preferred. Polyimide, polyester (e.g., polyethylene terephthalate (PET)) or cellulose release film is different from widely used polypropylene (PP), polyethylene (PE) and other heat-resistant polyolefins. Different from the separator, it is not only excellent in its own heat resistance, but also excellent in wettability to γ-butyrolactone (GBL). Therefore, the electrolytic solution 24 containing GBL (without rejection) can be sufficiently penetrated into the separator 18. As a result, the heat resistance of the lithium secondary battery 10 can be further improved. A particularly good release film is a release film made of polyimide. Polyimide separators are commercially available. Due to their extremely complex microstructures, they have the ability to more effectively prevent or delay the extension of lithium dendritic crystals precipitated during overcharge and short circuits caused by such extensions. On the other hand, cellulose-based separators have the advantage that they are cheaper than polyamido-based separators.

The thickness of the lithium secondary battery 10 is preferably 0.45 mm or less, preferably 0.1 to 0.45 mm, more preferably 0.2 to 0.45 mm, and particularly preferably 0.3 to 0.40 mm. When the thickness is in this range, it can be configured as a thin lithium battery suitable for being built in a thin device such as a smart card.

As shown in FIG. 1, the contents of the lithium secondary battery 10, that is, the battery element 12 and the electrolyte 24 are preferably covered and sealed with an outer coating film 26. That is, the lithium secondary battery 10 is preferably in the form of a battery called a so-called outer cover film. Here, the battery element 12 is defined as including a positive electrode plate 16, a separator 18, and a negative electrode 20, and typically includes a positive electrode current collector 14 and a negative electrode current collector 22. The positive electrode current collector 14 and the negative electrode current collector 22 are not particularly limited, but copper foil is preferred. The positive electrode terminal 15 is preferably provided on the positive electrode current collector 14 in a form extending from the positive electrode current collector 14, and the negative electrode terminal 23 is preferably provided on the negative electrode current collector 22 in a form extending from the negative electrode current collector 22. In addition, in FIG. 1, in order to show the existence of the electrolytic solution 24 for easy understanding, the lithium secondary battery 10 is depicted with a space allowance in the laminated structure and the seal structure. Actually, it is desirable to use such a space allowance. minimize. The outer edge of the lithium secondary battery 10 is sealed by thermally fusing the outer coating films 26. Sealing by heat fusion should be performed using a heat seal (also called a heating strip) generally used for heat sealing purposes.

The outer cover film 26 may be any commercially available outer cover film. The thickness of the outer coating film 26 is preferably 20 to 160 μm, more preferably 40 to 120 μm, and even more preferably 40 to 65 μm. The outer cover film 26 is preferably a laminated film containing a resin film and a metal foil, and more preferably a laminated film containing a resin film and an aluminum foil. The laminated film is preferably provided with a resin film on both sides of a metal foil such as aluminum foil. At this time, the resin film on one side of the metal foil (hereinafter referred to as the surface protective film) is preferably made of nylon, polyamine, polyethylene terephthalate, polyimide, polytetrafluoroethylene, polychlorotrifluoro Materials such as ethylene are excellent in reinforcement. The resin film on the other side of the metal foil (hereinafter referred to as a sealing resin film) is made of a heat-sealable material such as polypropylene. The aluminum laminated film of such a layer structure of surface protection film / aluminum foil / sealing resin film is sold on the market for lithium batteries, and the commercially available aluminum laminated film sealing resin film has a two-layer structure of polypropylene resin. This two-layer structure is generally composed of a main layer having a softening point of 150 to 160 ° C and an adhesive layer having a softening point of 130 to 140 ° C that exists outside the main layer. However, since the softening point of the adhesive layer at a softening point of 130 to 140 ° C is lower than that of the main layer, it is easy to soften or flow due to heating, so it can be said that the heat resistance is poor. Therefore, from the viewpoint of improving the heat resistance of the lithium secondary battery 10, the following improvement of i) or ii) is preferably performed on the sealing resin film of the two-layer structure of the polypropylene resin.
i) A sealing resin film having a single-layer structure without a bonding layer and having only a main layer. By doing so, since there is no adhesive layer having a softening point of 130 to 140 ° C, heat resistance is improved. At this time, the main layer with a softening point of 150 to 160 ° C also functions as an adhesive layer.
ii) A heat-resistant polypropylene film without a bonding layer and a high softening temperature is used as the main layer. It is known that a heat-resistant polypropylene film having a softening temperature as high as 160 to 170 ° C. By using a single-layer structure of the heat-resistant polypropylene film as the sealing resin film, the highest heat resistance of polypropylene can be ensured.

In addition, in order to prevent the outer cover film 26 from being cracked under heat and pressure such as thermal lamination, it may be applied to at least one of the positive electrode current collector 14, the positive electrode terminal 15, the negative electrode current collector 22, and the negative electrode terminal 23. Attach a protective tape. By doing so, it is possible to effectively prevent the outer cover film 26 from being broken due to a burr that may be formed at the end of the member. Preferred examples of the protective tape include polyimide tape as an example in terms of excellent heat resistance.

[Manufacturing method of lithium cobaltate sintered plate]
The oriented positive electrode plate and the oriented sintered plate suitable for the lithium secondary battery of the present invention can be manufactured by any manufacturing method, preferably as exemplified below, (1) LiCoO ₂ template particle production, (2) matrix particle production, (3) Production of raw embryos and (4) Production of oriented sintered plates.

(1) Preparation of LiCoO ₂ template particles: Co ₃ O ₄ raw material powder and Li ₂ CO ₃ raw material powder are mixed. The obtained mixed powder is fired at 500 to 900 ° C for 1 to 20 hours to synthesize LiCoO ₂ powder. The obtained LiCoO ₂ powder was pulverized by a ball mill into a volume-based D50 particle size of 0.1 to 10 μm to obtain plate-shaped LiCoO ₂ particles capable of conducting lithium ions in parallel with the plate surface. The obtained LiCoO ₂ particles are formed in a state that is easy to cleave along the cleavage plane. LiCoO ₂ particles are crushed and cleaved to produce LiCoO ₂ template particles. Such LiCoO ₂ particles can also be synthesized by the method of crushing and growing the raw embryo grains using LiCoO ₂ powder slurry, using the flux method, hydrothermal synthesis or single crystal growth of the melt, and the sol-gel method. Obtained by the method of plate crystal.

In this process, the shape of the primary particles constituting the oriented positive electrode plate 16 can be controlled as follows.
- by adjusting the aspect ratio and size of the LiCoO ₂ particles at least one template can be controlled angle of orientation of the particles is greater than the aspect ratio of the template 030LiCoO _2, and that the larger the particle diameter of particles of LiCoO ₂ template, can improve the Total area ratio of low-angle primary particles. The aspect ratio and particle size of the LiCoO ₂ template particles can be adjusted by adjusting the particle size of the Co ₃ O ₄ raw material powder and Li ₂ CO ₃ raw material powder, the pulverizing conditions (pulverizing time, pulverizing energy, pulverizing method, etc.) and pulverizing Control of at least one of the latter classifications.
-By adjusting the aspect ratio of the LiCoO ₂ template particles, the total area ratio of the primary particles 11 with an aspect ratio of 4 or more can be controlled. Specifically, the larger the aspect ratio of the LiCoO ₂ template particles, the more the total area ratio of the primary particles having an aspect ratio of 4 or more can be increased. The method of adjusting the aspect ratio of the LiCoO ₂ template particles is as described above.
-By adjusting the particle diameter of the LiCoO ₂ template particles, the average particle diameter of the primary particles 11 can be controlled.
-By adjusting the particle diameter of the LiCoO ₂ template particles, the density of the positive electrode plate 16 can be controlled. Specifically, the smaller the particle diameter of the LiCoO ₂ template particles, the more dense the oriented positive electrode plate 16 can be.

(2) Preparation of matrix particles Co ₃ O ₄ raw material powder was used as matrix particles. The volume-based D50 particle size of the Co ₃ O ₄ raw material powder is not particularly limited, and may be, for example, 0.1 to 1.0 μm, and is preferably smaller than the volume-based D50 particle size of the LiCoO ₂ template particles. The matrix particles can also be obtained by heat-treating the Co (OH) ₂ raw material at 500-800 ° C for 1-10 hours. In addition to the matrix particles, Co (OH) ₂ particles may be used in addition to Co ₃ O ₄ , and LiCoO ₂ particles may also be used.

In this process, the outer shape of the primary particles 11 constituting the oriented positive electrode plate 16 can be controlled as follows.
-By adjusting the ratio of the particle size of the matrix particles to the particle size of the LiCoO ₂ template particles (hereinafter referred to as "matrix / template ratio"), the orientation angle can be controlled to exceed 030 to make the matrix / template particle size ratio smaller, that is, the matrix particles The smaller the particle size, the easier it is to take matrix particles into LiCoO ₂ template particles in the firing process described later, so the total area ratio of low-angle primary particles can be increased.
-By adjusting the matrix / template particle size ratio, the total area ratio of the primary particles 11 with an aspect ratio of 4 or more can be controlled. Specifically, the smaller the matrix / template particle size ratio, that is, the smaller the particle size of the matrix particles, the more the total area ratio of the primary particles 11 having an aspect ratio of 4 or more can be increased.
-The density of the oriented positive electrode plate 16 can be controlled by adjusting the matrix / template particle size ratio. Specifically, the smaller the matrix / template particle size ratio, that is, the smaller the particle size of the matrix particles, the more dense the oriented positive electrode plate 16 can be.

(3) Production of raw embryos LiCoO ₂ template particles and matrix particles were mixed into 100: 3 to 3:97 to obtain a mixed powder. While mixing this mixed powder, dispersing medium, binder, plasticizer and dispersant, while stirring and degassing under reduced pressure, adjusting to the desired viscosity to form a slurry. Next, the prepared slurry is formed into a formed body by a forming method capable of applying a shearing force to the LiCoO ₂ template particles. In this way, the blade forming method is suitable as a shaping method in which the average orientation angle of each primary particle 11 exceeds 030 LiCoO _{2 and the} template particles are applied with a shear force. When the doctor blade method is used, the prepared slurry is formed on a PET film to form a green embryo as a formed body.

In this process, the shape of the primary particles 11 constituting the oriented positive electrode plate 16 can be controlled as follows.
-By adjusting the forming speed, the orientation angle can be controlled to exceed 030
-By adjusting the density of the formed body, the average particle diameter of the primary particles 11 can be controlled. Specifically, the larger the density of the formed body, the larger the average particle diameter of the primary particles 11 can be.
-By adjusting the mixing ratio of the LiCoO ₂ template particles to the matrix particles, the density of the oriented positive electrode plate 16 can also be controlled. Specifically, as the number of LiCoO ₂ template particles is increased, the density of the oriented positive electrode plate 16 can be reduced.

(4) Preparation of oriented sintered plate The molded body of the slurry was placed in a zirconia bracket and subjected to heat treatment (one firing) at 500 to 900 ° C for 1 to 10 hours to obtain a sintered plate as an intermediate. This sintered plate was placed on a zirconia bracket in a state of being held upside down by a lithium sheet (for example, a sheet containing Li ₂ CO ₃ ) and subjected to secondary firing to obtain a LiCoO ₂ sintered plate. Specifically, a bracket on which a sintered plate held by a lithium sheet is placed in an alumina sheath, and then sintered at 700 to 850 ° C for 1 to 20 hours in the atmosphere, and then the sintered plate is again subjected to a lithium sheet. LiCoO ₂ sintered plate was obtained by sintering at 750 to 900 ° C. for 1 to 40 hours. This firing process can be divided into two times and one time. When divided into two firings, the firing temperature of the first firing should be lower than the firing temperature of the second firing. In addition, the total used amount of the secondary-fired lithium flakes may be 1.0 as long as the molar ratio of the amount of Li in the green embryo and the amount of Co in the green embryo to the amount of Co in the green embryo is 1.0.

In this process, the shape of the primary particles 11 constituting the oriented positive electrode plate 16 can be controlled as follows.
-By adjusting the heating rate during firing, the orientation angle can be controlled to sinter over 030 matrix particles, and the total area ratio of low-angle primary particles can be increased.
-By adjusting the heat treatment temperature of the intermediate, it is also possible to control the orientation angle to be lower than the heat treatment temperature of the 030 intermediate, the lower the sintering of the matrix particles can be suppressed, and the total area ratio of the low-angle primary particles can be increased.
-The average particle diameter of the primary particles 11 can be controlled by adjusting at least one of the heating rate during firing and the heat treatment temperature of the intermediate. Specifically, the faster the temperature increase rate and the lower the heat treatment temperature of the intermediate, the larger the average particle diameter of the primary particles 11 can be.
-By adjusting at least one of the amount of Li (such as Li ₂ CO ₃ ) and the amount of sintering aid (such as boric acid or bismuth oxide) during firing, the average particle diameter of the primary particles 11 can also be controlled. Specifically, the larger the Li amount and the larger the sintering aid amount, the larger the average particle diameter of the primary particles 11 can be.
-By adjusting the outer shape during firing, the density of the oriented positive electrode plate 16 can be controlled. Specifically, the slower the firing speed and the longer the firing time, the more dense the directional positive electrode plate 16 can be.
[Example]

The present invention will be described more specifically by the following examples.

[Example A1]
(1) Production of Lithium Secondary Battery A lithium secondary battery 10 schematically showing the form of a battery with an outer coating film as shown in FIG. 1 was produced using the procedures shown in FIGS. 2A and 2B. The details are as follows.

First, a sintered LiCoO ₂ plate (hereinafter referred to as an LCO sintered plate) having a thickness of 90 μm was prepared. This LCO sintered plate is manufactured according to the aforementioned manufacturing method of the lithium composite oxide sintered plate, and satisfies the preferable conditions of the foregoing lithium composite oxide sintered plate. This sintered plate was cut into a square of 10 mm × 10 mm square by a laser processing machine to obtain a plurality of small plate-shaped positive electrode plates 16.

As the outer cover film 26, two alumina laminated films (three-layer structure made of Showa Denko Packaging, thickness 61 μm, polypropylene film / aluminum box / nylon film) were prepared. As shown in FIG. 2A, a plurality of small sheet-shaped positive electrode plates 16 are laminated on a single outer-layer coating film 26 via a positive electrode current collector 14 (a copper foil having a thickness of 9 μm) to form a positive electrode assembly 17. At this time, the positive electrode current collector 14 is fixed to the outer-layer coating film 26 with an adhesive. In addition, the positive electrode terminal 15 is fixed to the positive electrode current collector 14 by welding to extend from the positive electrode current collector 14. On the other hand, a negative electrode 20 (a copper foil having a thickness of 10 μm) is laminated with a negative electrode 20 (a carbon layer having a thickness of 130 μm) on another outer cover film 26 to constitute a negative electrode assembly 19. At this time, the negative electrode current collector 22 is fixed to the outer-layer coating film 26 with an adhesive. The negative electrode terminal 23 is fixed to the negative electrode current collector 22 by welding to extend from the negative electrode current collector 22. As shown in Table 1, the carbon layer as the negative electrode 20 is a coating film containing a mixture of graphite as an active material and styrene butadiene rubber (SBR) as a binder.

A porous polyimide film (manufactured by Tokyo Yingka Co., Ltd., having a thickness of 23 μm and a porosity of 80%) was prepared as the separator 18. As shown in FIG. 2A, the positive electrode assembly 17, the separator 18, and the negative electrode assembly 19 are sequentially laminated so that the positive electrode plate 16 and the negative electrode 20 are opposed to the separator film 18, so that an outer layer covering film 26 covering both sides and an outer layer The laminated body 28 whose outer peripheral portion of the coating film 26 is exposed from the outer edge of the battery element 12. The thickness of the battery element 12 (the positive electrode current collector 14, the positive electrode plate 16, the separator 18, the negative electrode 20, and the negative electrode current collector 22) constructed in the laminated body 28 in this manner is 0.33 mm, and its shape and size are 2.3 cm × 3.2cm square.

As shown in FIG. 2A, the three sides A of the obtained laminated body 28 were sealed. This sealing is performed by heating and pressing the outer peripheral portion of the laminated body 28 at 200 ° C. and 1.5 MPa for 10 seconds, and thermally fusing the outer cover films 26 (aluminum laminated film) at the outer peripheral portion. After sealing at three sides A, the laminated body 28 was put into a vacuum dryer 34 to remove moisture and dry the adhesive.

As shown in FIG. 2B, in the glove box 38, a gap B between the outer cover film 26 is formed on the unsealed remaining side B of the laminated body 28 that has been sealed on three sides A of the outer edge, and an injection device is inserted into the gap. 36. The electrolyte 24 is injected, and the side B is temporarily sealed under a decompressed gas environment with an absolute pressure of 5 kPa. The electrolytic solution used was an electrolytic solution in which LiBF ₄ was dissolved at a concentration of 1.5 mol / L in a mixed solvent containing ethylene carbonate (EC) and γ-butyrolactone (GBL) in a ratio of 1: 3 (volume ratio). The laminated body thus sealed with edge B was subjected to initial charging, and was aged for 7 days. After cutting off the outer peripheral portion of the remaining one side B (the end portion excluding the battery element), degassing is performed.

As shown in FIG. 2B, in the glove box 38, the side B 'produced by the temporary sealing cut-off is performed in a decompressed gas environment with an absolute pressure of 5 kPa. This sealing is also performed by heating and pressing the outer peripheral portion of the laminated body 28 at 200 ° C. and 1.5 MPa for 10 seconds, and thermally fusing the outer coating films 26 (aluminum laminated film) at the outer peripheral portion. In this manner, the lithium secondary battery 10 having the form of a battery with an outer cover film 1 sealed with the outer cover film 26 on the side B 'is configured. The lithium secondary battery 10 was taken out of the glove box 38, and the unnecessary portions on the outer periphery of the outer coating film 26 were cut away to adjust the shape of the lithium secondary battery 10. In this manner, a lithium secondary battery 10 was obtained in which an outer cover film 26 was used to seal the outer edge 4 sides of the battery element 12 and the electrolyte solution 24 was injected. The obtained lithium secondary battery 10 has a rectangular shape with a size of 38 mm × 27 mm, a thickness of 0.45 mm or less, and a capacity of 30 mAh.

(2) Assess the heating and pressure of the produced lithium secondary battery at a temperature of 20 ℃, 100 ℃, 110 ℃, 120 ℃, or 150 ℃ for 30 minutes and a pressure of 0.7 MPa in a hot press device. After pressing, the following evaluations were performed.

＜ Battery appearance ＞
The presence or absence of a change in the appearance of the battery was observed by visual observation of the lithium secondary battery that had been heated as described above. The results are shown in Table 1A. No change in the appearance of the battery was observed at any heating temperature.

＜ Battery resistance ＞
The electrochemical resistance system SP-150 manufactured by BioLogic was used to measure the battery resistance of the lithium secondary battery subjected to the above-mentioned heating by an AC impedance method. The measured battery resistance was calculated as a relative value when the battery resistance of a battery heated at 20 ° C was 1. The results are shown in Table 1A. No change in battery resistance was observed at any heating temperature compared to a battery with a heating temperature of 20 ° C.

[Example A2] (comparative)
i) A coating film (hereinafter referred to as an LCO coating electrode) using a mixture of LiCoO ₂ powder and polydifluoroethylene (PVDF) as a positive electrode instead of an LCO sintered plate, and ii) an electrolyte using LiPF ₆ at 3: 7 (Volume ratio) A mixed solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) is dissolved into an electrolyte having a concentration of 1 mol / L, and iii) polydifluoroethylene (PVDF) is used as a negative electrode binder instead of SBR. Except for this, the battery was manufactured and evaluated in the same manner as in Example A1. The results are shown in Table 1A.

[Example A3] (comparative)
As the electrolytic solution, an electrolytic solution in which LiPF ₆ was dissolved in a mixed solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) at a ratio of 3: 7 (volume ratio) to 1 mol / L was used. The battery was fabricated and evaluated in the same manner as in Example A2. The results are shown in Table 1A.

[Example A4] (comparative)
i) The electrolytic solution uses an electrolytic solution in which LiPF _{6 is} dissolved in a mixed solvent containing ethyl carbonate (EC) and ethyl methyl carbonate (EMC) at a ratio of 3: 7 (volume ratio) to a concentration of 1 mol / L, and ii ) The battery was produced and evaluated in the same manner as in Example A1 except that the negative electrode binder used polydifluoroethylene (PVDF) instead of SBR. The results are shown in Table 1A.

[Example A5] (comparative)
As the electrolytic solution, an electrolytic solution in which LiPF ₆ was dissolved in a mixed solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) at a ratio of 3: 7 (volume ratio) to 1 mol / L was used. The battery was fabricated and evaluated in the same manner as in Example A4. The results are shown in Table 1A.

[Example A6] (comparative)
As the electrolytic solution, an electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent containing ethyl carbonate (EC) and ethyl methyl carbonate (EMC) at a ratio of 3: 7 (volume ratio) was used. The battery was fabricated and evaluated in the same manner as in Example A1. The results are shown in Table 1A.

[Example A7] (comparative)
As the electrolytic solution, an electrolytic solution in which LiPF ₆ was dissolved in a mixed solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) at a ratio of 3: 7 (volume ratio) to 1 mol / L was used. The battery was fabricated and evaluated in the same manner as in Example A1. The results are shown in Table 1A.

[Example A8] (comparative)
i) the positive electrode uses a coating of LiCoO ₂ powder and a mixture of polyvinylidene fluoride (PVDF) (that is, an LCO coated electrode) to replace the LCO sintered plate, and ii) the negative electrode binder uses polydifluoroethylene (PVDF) A battery was produced and evaluated in the same manner as in Example A1 except that instead of SBR. The results are shown in Table 1B.

[Example A9] (comparative)
In addition to the use of a coating of a mixture of LiCoO ₂ powder and polyvinylidene fluoride (PVDF) (that is, an LCO-coated electrode) for the positive electrode, the LCO sintered plate was replaced in the same manner as in Example A1. Evaluation. The results are shown in Table 1B.

[Example A10] (comparative)
A negative electrode binder was produced and evaluated in the same manner as in Example A1, except that polydifluoroethylene (PVDF) was used instead of SBR. The results are shown in Table 1B.

[Example A11] (comparative)
The electrolyte used was LiBF ₄ dissolved in a mixed solvent containing propylene carbonate (PC) and γ-butyrolactone (GBL) at a ratio of 1: 3 (volume ratio) to a concentration of 1.5 mol / L. In addition, battery production and evaluation were performed in the same manner as in Example A10. The results are shown in Table 1B.

[Example A12] (comparative)
The electrolyte used was LiBF ₄ dissolved in a mixed solvent containing propylene carbonate (PC) and γ-butyrolactone (GBL) at a ratio of 1: 3 (volume ratio) to a concentration of 1.5 mol / L. The battery was produced and evaluated in the same manner as in Example A1. The results are shown in Table 1B.

[Table 1A]

[Table 1B]

10‧‧‧ lithium secondary battery

11‧‧‧ primary particle

14‧‧‧Positive collector

15‧‧‧Positive terminal

16‧‧‧Positive plate

17‧‧‧Positive electrode assembly

18‧‧‧ isolation film

19‧‧‧ Negative electrode assembly

20‧‧‧ Negative

22‧‧‧ negative current collector

23‧‧‧ Negative terminal

24‧‧‧ Electrolyte

26‧‧‧ Outer Cover Film

28‧‧‧layer

36‧‧‧ Injection Device

38‧‧‧Glove Box

A‧‧‧ side

B‧‧‧ side

B’‧‧‧ side

FIG. 1 is a schematic cross-sectional view of an example of a lithium secondary battery of the present invention.

FIG. 2A is a diagram showing the first half of an example of a manufacturing process of a lithium secondary battery.

FIG. 2B is a second half of an example of a manufacturing process of a lithium secondary battery, and is a diagram of a process following the process shown in FIG. 2A. FIG. 2B is a photograph of a battery including an outer cover film on the right end.

FIG. 3 is an SEM image showing an example of a cross section perpendicular to the plate surface of the oriented positive electrode plate.

FIG. 4 is an EBSD image of a cross section of the oriented positive electrode plate shown in FIG. 3.

FIG. 5 is a histogram showing the distribution of the orientation angle of the primary particles of the EBSD image of FIG. 4 on an area basis.

Claims (14)

A lithium secondary battery includes: a positive electrode plate, which is a lithium composite oxide sintered plate; a negative electrode, which contains carbon and styrene butadiene rubber (SBR); and an electrolyte, which is made of γ-butyrolactone (GBL ) Or non-aqueous solvent consisting of γ-butyrolactone (GBL) and ethyl carbonate (EC) contains lithium tetrafluoroborate (LiBF ₄ ). For example, the lithium secondary battery in item 1 of the patent application scope further includes: Polyimide, polyester or cellulose insulation film. For example, the lithium secondary battery in the second scope of the patent application, wherein: The separator is made of polyimide. For example, if a lithium secondary battery according to any one of the scope of claims 1 to 3 is applied for, The electrolyte further includes vinylene carbonate (VC) and / or fluoroethylene carbonate (FEC) and / or ethylene ethylene carbonate (VEC). For example, a lithium secondary battery in any one of the scope of claims 1 to 4, in which: The EC: GBL volume ratio of the non-aqueous solvent is from 0: 1 to 1: 1. For example, the lithium secondary battery according to any one of claims 1 to 5 of the patent application scope, wherein the LiBF ₄ concentration of the electrolytic solution is 0.5 to 2 mol / L. For example, a lithium secondary battery according to any one of the scope of claims 1 to 6, in which: The thickness of the lithium secondary battery is 0.45 mm or less. For example, for a lithium secondary battery in any one of the scope of claims 1 to 7, in which: The lithium composite oxide is lithium cobaltate. For example, a lithium secondary battery according to any one of the items 1 to 8 of the patent application scope, wherein: The lithium composite oxide sintered plate is a directional positive electrode plate having a plurality of primary particles composed of the lithium composite oxide, and the plurality of primary particles has a surface of the positive electrode plate exceeding 030. For example, a lithium secondary battery according to any one of the scope of claims 1 to 9, in which: This lithium secondary battery is intended to be mounted on a substrate in a procedure accompanied by heating at 110 ° C. or higher and less than 260 ° C. For example, the lithium secondary battery under the scope of patent application No. 10, wherein: The process accompanied by heating is a process of thermal lamination or a process with reflow. A method for manufacturing a built-in battery device includes the following steps: (1) Prepare a lithium secondary battery as described in any one of the scope of patent application items 1 to 11; (2) The lithium secondary battery is mounted on a substrate via a procedure accompanied by heating at 110 ° C or higher and less than 260 ° C. For example, a method for manufacturing a device with a built-in battery within the scope of application for patent No. 12, wherein: The process accompanied by heating is a process of thermal lamination or a process with reflow. For example, a method for manufacturing a device with a built-in battery within the scope of patent application item 13, wherein, The process accompanied by heating is a thermal lamination process, and the device with a built-in battery is a smart card with a built-in battery.